Approximate Nonlinear Modeling of Aircraft Engine Surge Margin Based on Equilibrium Manifold Expansion

Stable operation of aircraft engine compressions is constrained by rotating surge. In this paper, an approximate nonlinear surge margin model of aircraft engine compression system by using equilibrium manifold is presented. Firstly, this paper gives an overview of the current state of modeling aerodynamic flow instabilities in engine compressors. Secondly, the expansion form of equilibrium manifold is introduced, and the choosing scheduling variable method is discussed. Then, this paper also gives the identification procedure of modeling the approximate nonlinear model. Finally, the modeling and simulations with high pressure （liP） compressor surge margin of the aircraft engine show that this real-time model has the same accuracy with the thermody- namic model, but has simpler structure and shorter computation time.

Design of a high-performance centrifugal compressor with new surge margin improvement technique for high speed turbomachinery

This paper presents the design of a centrifugal compressor for high-speed turbomachinery.The main focus of the research is to develop a centrifugal compressor with improved aerodynamic performance.As a meridional frame has a significant effect on overall performance of the compressor,special attention has been paid to the end wall contours.The shroud profile is design with bezier curve and hub profile with circular arc contour.The blade angle distribution has been arranged in a manner that it merges with single value at impeller exit.The rake angle is positive at leading edge and negative at trailing edge with identical magnitude.Furthermore,three-dimensional straight line element approach has been used for this design for better manufacturability.The verification of the aerodynamic performance has been carried out using CFD software with consideration of a single blade passage and vaneless diffuser.The result has been compared with matching size aftermarket compressor stage gas stand data.The compressor stage with Trim 55 provides 34%increase in choke flow at 210000 RPM as compared to gas stand data with 87%peak stage efficiency at 110000 RPM.In addition,new surge margin improvement technique has been proposed by means of diffuser enhancement.This technique provides an average of 16%improvement in surge margin compared to standard diffuser stage with 55 trim compressor impeller.The mechanical integrity has been validated at maximum RPM with the aluminum alloy 2014-T6 as a fabrication material.

Improvement of part-load performance of gas turbine by adjusting compressor inlet air temperature and IGV opening

A novel adjusting method for improving gas turbine(GT)efficiency and surge margin(SM)under partload conditions is proposed.This method adopts the inlet air heating technology,which uses the waste heat of lowgrade heat source and the inlet guide vane(IGV)opening adjustment.Moreover,the regulation rules of the compressor inlet air temperature and the IGV opening are studied comprehensively to optimize GT performance.A model and calculation method for an equilibrium running line is adopted based on the characteristic curves of the compressor and turbine.The equilibrium running lines calculated through the calculation method involve three part-load conditions and three IGVopenings with different inlet air temperatures.The results show that there is an optimal matching relationship between IGV opening and inlet air temperature.For the best GT performance of a given load,the IGV could be adjusted according to inlet air temperature.In addition,inlet air heating has a considerable potential for the improvement of part-load performance of GT due to the increase in compressor efficiency,combustion efficiency,and turbine efficiency as well as turbine inlet temperature,when inlet air temperature is lower than the optimal value with different IGV openings.Further,when the IGV is in a full opening state and an optimal inlet air temperature is achieved by using the inlet air heating technology,GT efficiency and SM can be obviously higher than other IGVopenings.The IGV can be left unadjusted,even when the load is as low as 50%.These findings indicate that inlet air heating has a great potential to replace the IGV to regulate load because GT efficiency and SM can be remarkably improved,which is different from the traditional viewpoints.